In fuel delivery systems for gas turbine engines, it is well known to bypass a certain portion of the pumped flow by using the pressure differential generated across a fuel metering valve. Examples of bypass valves with differential pistons to provide compensating area to adjust for different system pressures are shown, for example, in Wernberg, U.S. Pat. No. 4,458,713 and Kao et al., U.S. Pat. No. 5,433,237, the full disclosures of which are hereby incorporated by reference.
Additionally, the state of the art also includes more recent attempts at providing a variable displacement pump fuel metering scheme which use a proportional and integral control valve to bypass pump flow and regulate pump flow. Examples of these types of systems are shown, for example, in Bennett et al., U.S. Pat. No. 6,962,485 and Reuter et al., U.S. Pat. No. 5,715,674, the disclosures of which are also hereby incorporated by reference.